1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile machine or similar electrophotographic image forming apparatus, and more particularly, the invention relates to a method and an apparatus for detecting developing ability of an image forming apparatus.
2. Discussion of Background
It is necessary for a conventional image forming apparatus to detect its own developing ability precisely. In order to detect developing ability of the image forming apparatus, intensity (A) of reflected light from the surface of an image bearing member, such as a photoconductive member or an intermediate transfer belt, and intensity (B) of reflected light from a reference toner image are detected by a photo-sensor. A ratio of intensities A and B is calculated (i.e. ratio=A/B), and the calculated ratio is compared to a reference value. As a result of this ratio calculation, a developing ability, such as toner adhering quantity on the image bearing member, is detected. In order to maintain a good image quality, image processing devices of the image forming apparatus, such as a charger, an exposure device, a developing device, etc. are controlled in response to the calculated ratio (i.e., developing ability).
Japanese Laid-Open Patent No. 04-60567 discloses a toner density control device in which a light-emitting device, such as a light-emitting diode, emits light only when the reflected light from the surface of the photoconductive drum is detected in order to extend the life of the light-emitting device and to prevent fatigue of the photoconductive member. The intensity of light of the light-emitting device varies corresponding to the continuous lighting time of the light-emitting diode. Namely, the intensity of light of the light-emitting diode decreases after the intensity of light reaches a maximum, since internal resistant value increases corresponding to an increase of internal temperature of the light-emitting diode. As a result, a detecting voltage of the toner pattern varies in response to the continuous lighting time of the light-emitting diode even if the density of the toner pattern is the same.